Basic and Diluted Net Loss Per Share - Computation of Company's Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net loss attributable to stockholders	$ (58,330)	$ (56,034)	$ (55,790)
Net loss attributable to common stockholders, basic	(58,330)	(56,034)	(55,790)
Net loss attributable to common stockholders, diluted	$ (58,330)	$ (56,034)	$ (55,790)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic	97,200,925	93,333,880	79,781,976
Weighted-average shares used to compute net loss per share attributable to common stockholders, diluted	97,200,925	93,333,880	79,781,976
Net loss per share attributable to common stockholders, basic	$ (0.60)	$ (0.60)	$ (0.70)
Net loss per share attributable to common stockholders, diluted	$ (0.60)	$ (0.60)	$ (0.70)